The present invention relates to photographic coupler compositions comprising two-equivalent 3-anilino-1-phenyl-5-pyrazolone magenta dye forming couplers with strong electron-withdrawing substituents on both the 3-anilino and 1-phenyl groups and with arylthio or alkylthio coupling-off groups. The invention also relates to color photographic materials including such coupler compositions and to methods for improving the hue of magenta dyes and for providing high dye formation efficiency in such materials.
There is considerable interest in using pyrazolone magenta couplers, particularly 3-anilino-1-phenyl-5-pyrazolone couplers, as imaging couplers for photographic applications. Advantages that may be associated with the use of these couplers include low cost, high reactivity, high dye extinction coefficients and good dispersibility. Two-equivalent pyrazolone magenta dye-forming couplers with coupling-off groups in the 4-position have additional potential advantages including high efficiency of dye formation from oxidized developer, very high reactivity, low sensitivity to process pH variations, formaldehyde insensitivity and resistance to thermally induced reaction with magenta dye. However, pyrazolone magenta dye forming couplers that previously have been described suffer from disadvantages such as producing dyes with hues that are too hypsochromic upon coupling with commonly used developers, high equivalency, sensitivity to formaldehyde or the tendency to undergo side reactions that do not lead to dye formation.
Dye hues that are too hypsochromic can lead to inaccurate and objectionable color reproduction from color negative materials or directly viewed photographic materials such as color prints or color transparencies. In color negative materials magenta dyes that are too hypsochromic produce high amounts of unwanted blue light absorption and can result in prints with inaccurate color or low color saturation. The unwanted blue absorption can also cause other negative effects such as increasing the time required to print from processed negatives by necessitating larger contents of masking couplers to offset the unwanted absorption and by limiting the amounts of other blue absorbers that can be added. The use of four-equivalent couplers or of two-equivalent couplers that undergo side reactions leads to inefficiencies and increases cost. This invention identifies practical two-equivalent magenta dye forming pyrazolone couplers and coupler compositions that have high activity, that are resistant to reaction with formaldehyde or to side reactions and that yield dyes with reduced unwanted blue light absorption for more accurate color reproduction. In addition, the coupler compositions of this invention can be used to produce photographic materials in which continued coupling is suitably low in processes without a stop bath between the development and bleach steps.
It is well known in the color photographic art that color images are produced by a colored dye that is formed by coupling reaction between an oxidized color developing agent and a coupler. Various improved 5-pyrazolone magenta-dye-forming couplers have been described since issuance of U.S. Pat. No. 1,969,479. Improvements that have been noted include substitution of halogen atoms or of alkoxy groups in the ortho position of the 3-anilino group for improved spectral properties, as described in British Patent GB 956,261. U.S. Pat. No. 3,928,044 describes the use of 3-anilino-5-pyrazolone couplers with alkoxycarbonyl groups in the meta or para positions of the 3-anilino ring, and U.S. Pat. No. 3,907,571 describes 3-anilino-5-pyrazolone magenta dye-forming couplers with sulfamoyl substituents in the meta or para positions of the anilino ring. However, the extent of the bathochromic hue shifts and of the reductions in unwanted blue light absorption by such dyes are less than normally desired for optimum color reproduction. Similarly, the couplers described in U.K. Patent Application 2,071,647 do not yield dyes that are sufficiently bathochromic for many applications.
U.S. Pat. Nos. 4,351,897 and 4,556,630 disclose two-equivalent 3-anilino-5-pyrazolone couplers with specific arylthio coupling-off groups. These patents do not consider structures that yield bathochromic dyes having low unwanted blue light absorption in accordance with the invention. German Patent Application DE 3,730,557 describes two-equivalent 3-anilino-5-pyrazolone couplers with thio coupling-off groups used in combination with carbonamide oil formers, but also does not deal with structures that yield bathochromic dyes with low unwanted blue light absorption.
Item 16736 in Research Disclosure, March 1978 describes 3-anilino-5-pyrazolone couplers with alkylsulfonyl substituents in the meta or para positions of the 3-anilino ring. These may also have alkylsulfonyl or arylsulfonyl substituents on the 1-phenyl group. However, examples of two-equivalent 3-anilino-5-pyrazolone couplers are not specifically included in this disclosure. U.K. Patent Specification 1,530,272 describes 3-anilino-1-phenyl-5-pyrazolone couplers with alkylsulfonyl or sulfamoyl substituents on the 1-phenyl group. These may also have strong electron-withdrawing sulfamoyl or carbamoyl substituents on the 3-anilino group. While various possible coupling-off groups are noted in U.K. Patent Specification 1,530,272, no specific structural examples with arylthio or alkylthio coupling-off groups are provided, and illustrative Examples 1 and 2 are restricted to four-equivalent couplers. Thus, U.K. Patent Specification 1,530,272 does not disclose couplers having the appropriate 3-anilino and 1-phenyl substituents as well as suitable coupling-off groups that provide all of the beneficial properties of the couplers of this invention.
U.S. Pat. No. 4,595,650 discloses photographic materials containing pyrazolone couplers of the 3-anilino or 3-acylamino types containing an arylthio group at the coupling position with an alkoxy or aryloxy substituent substituted in a specified manner. One of the 50 odd structures exemplified shows a strong electron withdrawing group in both rings but one of these is the undesirable acyl group. The use of acyl ring substituents is undesirable because these groups are difficult to synthesize, and they tend to be deleterious to the photographic properties, particularly light stability. No mention is made in the patent of the advantageous bathochromic properties obtained in this invention. Further, it has been found that arylthio coupling off groups containing an ortho alkoxy substituent exhibit undesirably stable leuco dyes.
In general, pyrazolone magenta couplers provide dyes that have the inherent property of absorbing some blue light which is undesirable because these dyes are ideally responsive to green light only. To keep the color record correct, it is necessary to include in the film a masking coupler which functions to provide a similar blue absorbance in the non-image areas corresponding to the unwanted blue absorbance in the image area caused by the magenta dye formed. Thus, the unwanted blue absorption is a problem which may require the addition of a mask. Also, the unwanted blue absorption adversely affects the ability to include image modifiers for sharpness etc. which generate dyes with unwanted blue absorption and also can prolong the printing time for processed negatives having the excess blue absorbance.
An embodiment of this invention relates to employing the photographic materials in combination with a dispersion of magnetic particles. U.S. Pat. No. 4,990,276 and EP 0 459 349 Al provide background on such dispersions and photographic materials. The coupler materials herein provide an effective way of counteracting unwanted blue light absorption by the magnetic layer in processed negatives during the printing of processed negatives.
It would be desirable to provide coupler compositions and color photographic materials having useful photographic properties and that yield bathochromic magenta dyes with reduced unwanted blue light absorption, particularly those that have high activity, that have low equivalency and that are free from side reactions, and which may be used for the efficient formation of magenta dyes in color photographic materials. It is further desirable to provide magenta dye forming coupler compositions and photographic materials of low cost, whose dye forming characteristics have low sensitivity to variations in developer pH, exhibit low continued coupling in seasoned bleach solutions, do not require stabilization with formaldehyde solutions and have stable magenta dye images, and which most preferably have a reduced tendency to form stable leuco dyes.